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Revealing quasars’ true colours

Revealing the true colours of quasars

Our astronomers have identified a rare moment in the life of some of the universe’s most energetic objects.

Now Durham University’s researchers have found a phase in the development of these galactic giants that could tell us more about how quasars and their host galaxies evolve.

Blue quasars

Quasars are powered by supermassive black holes at their centres and most appear blue in colour.

However, a significant number of quasars look red when viewed through the huge clouds of dust and gas that obscure them from view.

The conventional view of red quasars is that they are actually blue quasars that are angled away from our line-of-sight.

Red quasars

Our team has ruled out this model and instead has shown that red quasars are likely to be the result of a brief, but violent, phase in the evolution of galaxies when their black holes are ejecting large amounts of energy into the surrounding dust and gas.

This injection of energy blows away the dust and gas to reveal a blue quasar.

Our astronomers studied 10,000 red and blue quasars as they would have been seen seven to 11 billion years ago when the universe was relatively young.

Galaxy evolution

They say their research could also tell us more about galaxy evolution as they expect that the massive burst of energy from the black hole would burn off the gas needed to form stars.

Without gas, the galaxies can’t grow – so the quasar is effectively ending the life of the galaxy by destroying the very thing that it needs to survive.